Welcome to DU!
The truly grassroots left-of-center political community where regular people, not algorithms, drive the discussions and set the standards.
Join the community:
Create a free account
Support DU (and get rid of ads!):
Become a Star Member
Latest Breaking News
General Discussion
The DU Lounge
All Forums
Issue Forums
Culture Forums
Alliance Forums
Region Forums
Support Forums
Help & Search
Most of Greenland Ice Melted to Bedrock in Recent Geologic Past, Study Says
http://www.ldeo.columbia.edu/news-events/most-greenland-ice-melted-bedrock-recent-geologic-past-study-says[font face=Serif][font size=5]Most of Greenland Ice Melted to Bedrock in Recent Geologic Past, Study Says[/font]
December 7, 2016
[font size=4]Finding Suggests the Ice Sheet Is More Vulnerable than Thought[/font]
[font size=3]Scientists have found evidence in a chunk of bedrock drilled from nearly two miles below the summit of the Greenland Ice Sheet that the ice nearly disappeared for an extended time in the last million years or so. The finding casts doubt on assumptions that Greenland has been relatively stable during the recent geological past, and implies that global warming could tip it into decline more precipitously than previously thought. Such a decline could cause rapid sea-level rise. The findings appear this week in the leading journal Nature.
The study is based on perhaps Earth’s rarest geologic sample: the only bit of bedrock yet retrieved from the ice sheet’s base, more than two decades ago. The authors say that chemical isotopes in it indicate that the surface was exposed to open sky for at least 280,000 years during the last 1.4 million years. The reason would have been natural, probably tied to cyclic natural climate changes that have caused ice ages to wax and wane. The scientists say that in the most conservative interpretation, there might have been only one ice-free period that ended 1.1 million years ago. But, more likely, they say, the ice vanished multiple times for shorter periods closer to the present. Greenland contains about 684,000 cubic miles of ice – enough to raise global sea levels about 24 feet if it were to melt completely.
“Unfortunately, this makes the Greenland ice sheet look highly unstable,” said lead author Joerg Schaefer, a paleoclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “If we lost it in periods of natural forcing, we may lose it again.” With human-induced warming now well underway, loss of the Greenland ice has roughly doubled since the 1990s; during the last four years by some estimates, it shed more than a trillion tons.
No one knows exactly what it might take to make the ice collapse, or how long that might take. Some models project that it will melt partially or completely over the next 2,500 to 10,000 years, depending on the amount of greenhouse gases humans pour into the air. Ice loss from Greenland now accounts for about a quarter of the current sea-level rise, which is about 3 millimeters a year, but this could accelerate. Projections of sea-level rise during this century hover around 3 or 4 feet, but many, including the one from the Intergovernmental Panel on Climate Change, do not take Greenland into account. More drastic models put the potential rise much higher.
…
http://vimeo.com/194375492
…[/font][/font]
December 7, 2016
[font size=4]Finding Suggests the Ice Sheet Is More Vulnerable than Thought[/font]
[font size=3]Scientists have found evidence in a chunk of bedrock drilled from nearly two miles below the summit of the Greenland Ice Sheet that the ice nearly disappeared for an extended time in the last million years or so. The finding casts doubt on assumptions that Greenland has been relatively stable during the recent geological past, and implies that global warming could tip it into decline more precipitously than previously thought. Such a decline could cause rapid sea-level rise. The findings appear this week in the leading journal Nature.
The study is based on perhaps Earth’s rarest geologic sample: the only bit of bedrock yet retrieved from the ice sheet’s base, more than two decades ago. The authors say that chemical isotopes in it indicate that the surface was exposed to open sky for at least 280,000 years during the last 1.4 million years. The reason would have been natural, probably tied to cyclic natural climate changes that have caused ice ages to wax and wane. The scientists say that in the most conservative interpretation, there might have been only one ice-free period that ended 1.1 million years ago. But, more likely, they say, the ice vanished multiple times for shorter periods closer to the present. Greenland contains about 684,000 cubic miles of ice – enough to raise global sea levels about 24 feet if it were to melt completely.
“Unfortunately, this makes the Greenland ice sheet look highly unstable,” said lead author Joerg Schaefer, a paleoclimatologist at Columbia University’s Lamont-Doherty Earth Observatory. “If we lost it in periods of natural forcing, we may lose it again.” With human-induced warming now well underway, loss of the Greenland ice has roughly doubled since the 1990s; during the last four years by some estimates, it shed more than a trillion tons.
No one knows exactly what it might take to make the ice collapse, or how long that might take. Some models project that it will melt partially or completely over the next 2,500 to 10,000 years, depending on the amount of greenhouse gases humans pour into the air. Ice loss from Greenland now accounts for about a quarter of the current sea-level rise, which is about 3 millimeters a year, but this could accelerate. Projections of sea-level rise during this century hover around 3 or 4 feet, but many, including the one from the Intergovernmental Panel on Climate Change, do not take Greenland into account. More drastic models put the potential rise much higher.
…
http://vimeo.com/194375492
…[/font][/font]
https://www.llnl.gov/news/east-greenland-ice-sheet-has-responded-climate-change-last-75-million-years
[font face=Serif]Dec. 7, 2016
[font size=5]East Greenland ice sheet has responded to climate change for the last 7.5 million years[/font]
Anne M Stark
[font size=3]Using marine sediment cores containing isotopes of aluminum and beryllium, a group of international researchers has discovered that East Greenland experienced deep, ongoing glacial erosion over the past 7.5 million years.
The research reconstructs ice sheet erosion dynamics in that region during the past 7.5 million years and has potential implications for how much the ice sheet will respond to future interglacial warming.
…
Understanding of early Greenland glaciation remains fragmentary, uncertain and for some periods, contradictory; much of what is known comes from marine sediments. The first presence of ice-rafted debris suggests that East Greenland glaciers initially reached the coast about 7.5 million years ago, whereas the surface texture of the sand grains suggests that glaciation began 11 million years ago.
"The East Greenland ice sheet has been dynamic over the last 7.5 million years," said lead author and University of Vermont scientist Paul Bierman. "Greenland was mostly ice-covered during the mid-to-late Pleistocene. At major climate transitions, the ice sheet expanded into previously ice-free terrain, confirming that the East Greenland Ice Sheet consistently responded to global climate change."
…[/font][/font]
[font size=5]East Greenland ice sheet has responded to climate change for the last 7.5 million years[/font]
Anne M Stark
[font size=3]Using marine sediment cores containing isotopes of aluminum and beryllium, a group of international researchers has discovered that East Greenland experienced deep, ongoing glacial erosion over the past 7.5 million years.
The research reconstructs ice sheet erosion dynamics in that region during the past 7.5 million years and has potential implications for how much the ice sheet will respond to future interglacial warming.
…
Understanding of early Greenland glaciation remains fragmentary, uncertain and for some periods, contradictory; much of what is known comes from marine sediments. The first presence of ice-rafted debris suggests that East Greenland glaciers initially reached the coast about 7.5 million years ago, whereas the surface texture of the sand grains suggests that glaciation began 11 million years ago.
"The East Greenland ice sheet has been dynamic over the last 7.5 million years," said lead author and University of Vermont scientist Paul Bierman. "Greenland was mostly ice-covered during the mid-to-late Pleistocene. At major climate transitions, the ice sheet expanded into previously ice-free terrain, confirming that the East Greenland Ice Sheet consistently responded to global climate change."
…[/font][/font]
http://dx.doi.org/10.5194/acp-16-3761-2016
[font face=Serif]22 Mar 2016
[font size=5]Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous [/font]
[font size=3]Abstract. We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO₂, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO₂ change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.
…[/font][/font]
[font size=5]Ice melt, sea level rise and superstorms: evidence from paleoclimate data, climate modeling, and modern observations that 2 °C global warming could be dangerous [/font]
[font size=3]Abstract. We use numerical climate simulations, paleoclimate data, and modern observations to study the effect of growing ice melt from Antarctica and Greenland. Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration. We hypothesize that ice mass loss from the most vulnerable ice, sufficient to raise sea level several meters, is better approximated as exponential than by a more linear response. Doubling times of 10, 20 or 40 years yield multi-meter sea level rise in about 50, 100 or 200 years. Recent ice melt doubling times are near the lower end of the 10–40-year range, but the record is too short to confirm the nature of the response. The feedbacks, including subsurface ocean warming, help explain paleoclimate data and point to a dominant Southern Ocean role in controlling atmospheric CO₂, which in turn exercised tight control on global temperature and sea level. The millennial (500–2000-year) timescale of deep-ocean ventilation affects the timescale for natural CO₂ change and thus the timescale for paleo-global climate, ice sheet, and sea level changes, but this paleo-millennial timescale should not be misinterpreted as the timescale for ice sheet response to a rapid, large, human-made climate forcing. These climate feedbacks aid interpretation of events late in the prior interglacial, when sea level rose to +6–9 m with evidence of extreme storms while Earth was less than 1 °C warmer than today. Ice melt cooling of the North Atlantic and Southern oceans increases atmospheric temperature gradients, eddy kinetic energy and baroclinicity, thus driving more powerful storms. The modeling, paleoclimate evidence, and ongoing observations together imply that 2 °C global warming above the preindustrial level could be dangerous. Continued high fossil fuel emissions this century are predicted to yield (1) cooling of the Southern Ocean, especially in the Western Hemisphere; (2) slowing of the Southern Ocean overturning circulation, warming of the ice shelves, and growing ice sheet mass loss; (3) slowdown and eventual shutdown of the Atlantic overturning circulation with cooling of the North Atlantic region; (4) increasingly powerful storms; and (5) nonlinearly growing sea level rise, reaching several meters over a timescale of 50–150 years. These predictions, especially the cooling in the Southern Ocean and North Atlantic with markedly reduced warming or even cooling in Europe, differ fundamentally from existing climate change assessments. We discuss observations and modeling studies needed to refute or clarify these assertions.
…[/font][/font]
1 replies
= new reply since forum marked as read
= new reply since forum marked as read
